Equity Transactions (Detail) $ / shares in Units, $ in Thousands					3 Months Ended				12 Months Ended			87 Months Ended
	Feb. 15, 2018 USD ($) $ / shares	Feb. 01, 2018 USD ($)	Feb. 01, 2017 USD ($) day $ / shares shares	Jun. 08, 2016 shares	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 $ / shares	Jun. 30, 2017 $ / shares	Mar. 31, 2017 $ / shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares shares	Feb. 01, 2020 $ / shares shares	Feb. 24, 2017 $ / shares
Equity, Class of Treasury Stock [Line Items]
Common stock authorized to be repurchased (in shares)					4,200,000				4,200,000			4,200,000
Remaining common stock authorized for repurchase (in shares)										883,756
Repurchase of common shares (in shares)									66,244			3,852,805
Cost of shares repurchased | $									$ 7,500			$ 399,000
Weighted average price (in $ per share) | $ / shares												$ 103.55
Stock issued (in shares)									1,260,169
Cash dividends declared per common share (in $ per share) | $ / shares					$ 0.45	$ 0.45	$ 0.45	$ 0.45	$ 1.80	$ 1.8	$ 1.8
Cash dividends declared | $									$ 13,545	$ 13,015	$ 16,009
Cash dividends declared per preferred share (in $ per share) | $ / shares					$ 1.8125	$ 1.8125	$ 1.8125	$ 1.8125	$ 7.25	$ 0	$ 0
Cash dividends declared. preferred | $									$ 8,337
Dividends payable | $					$ 6,528				$ 6,528	$ 3,479		$ 6,528
Convertible preferred stock
Equity, Class of Treasury Stock [Line Items]
Stock issued (in shares)			1,150,000
Preferred stock dividend rate			7.25%
Preferred stock liquidation preference (in $ per share) | $ / shares			$ 100.00											$ 100
Preferred stock conversion, threshold consecutive trading days | day			20
Convertible preferred stock | Forecast | Minimum
Equity, Class of Treasury Stock [Line Items]
Preferred stock, shares issuable upon conversion (in shares)													0.7576
Conversion price of stock (USD per share) | $ / shares													$ 110
Convertible preferred stock | Forecast | Maximum
Equity, Class of Treasury Stock [Line Items]
Preferred stock, shares issuable upon conversion (in shares)													0.9091
Conversion price of stock (USD per share) | $ / shares													$ 132
Common Stock
Equity, Class of Treasury Stock [Line Items]
Net proceeds from stock issuance | $			$ 111,000
Subsequent Event
Equity, Class of Treasury Stock [Line Items]
Cash dividends declared per common share (in $ per share) | $ / shares	$ 0.45
Cash dividends declared | $	$ 4,400
Cash dividends declared per preferred share (in $ per share) | $ / shares	$ 1.8125
Cash dividends declared. preferred | $		$ 2,100
Stock Purchase Agreement
Equity, Class of Treasury Stock [Line Items]
Repurchase of common shares (in shares)										1,727,746
Cost of shares repurchased | $										$ 161,500
Weighted average price (in $ per share) | $ / shares										$ 93.50
Repurchase Plan, Tender Offer
Equity, Class of Treasury Stock [Line Items]
Repurchase of common shares (in shares)				556,516
Shares repurchased, percentage of common stock outstanding				6.70%
Public Offering
Equity, Class of Treasury Stock [Line Items]
Stock issued (in shares)									1,046,500
Proceeds received on sale of stock | $									$ 109,500
RidgeWorth
Equity, Class of Treasury Stock [Line Items]
Stock issued (in shares)									213,669
Additional Paid-in Capital
Equity, Class of Treasury Stock [Line Items]
Cash dividends declared | $									$ 13,545	$ 13,015	$ 16,009